Fluorescence quantum yields of isotopic CO 2+ ions

Abstract

Fluorescence quantum yields of the à 2Π u and B̃ 2Σ u + states of the isotopic ions 12C 16O 2 +, 13C 16O 2 + and 12C 18O 2 +, formed by 584 Å photoionization of CO 2, have been measured by a photon—photoion coincidence technique. The corresponding 584 Å photoelectron spectra, measured for 12C 16O 2 and 13C 16O 2, showed that the relative photoelectron branching ratios for forming the à 2Π u and B̃ 2Σ u + states of CO 2 + are isotope independent. The fluorescence quantum yields are greater than unity for the à 2Π u state and less than unity for B̃ 2Σ u + for the three isotopic ions but the values are isotopic dependent, the difference from unity correlating with the degree of spectral perturbation in the B̃ 2Σ u + − X̃ 2Π g 0 0 band. Calculations are made to identify the vibronic levels of à 2Π u capable of interacting with the B̃ 2Σ u + (0, 0, 0) level. The discrepancy concerning the apparent population ratio of the A 2Π u and B 2Σ u + states of CO 2 +, formed by photoionization of CO 2, between the results of photoelectron spectroscopy and those of CO 2 +, ion fluorescence intensities is explained as due to interelectronic state coupling. The effects of this discrepancy on the determination of cross sections for forming the B̃ 2Σ u + and à 2Π u states by various excitation mechanisms are discussed.